Lubiprostone (1) is an E1 type prostaglandin derivative. It is marketed in USA as Amitiza® and is used for the treatment of idiopathic chronic constipation, irritable bowel syndrome and post operative ilues. The use of Lubiprostone softens the stool, increases motility, and promotes spontaneous bowel movements (SBM). Chemically, Lubiprostone is 7-[(2R,4aR,5R,7aR)-2-(1,1-difluoropentyl)-2-hydroxy-6-oxooctahydrocyclopenta[b]pyran-5-yl]heptanoic acid (Drugs of the Future, 2004, 29(4); 336-341):

U.S. Pat. No. 5,117,042 discloses a method of treatment for improving encephalic function which comprises administering to a subject in need of such treatment a 15-keto-prostaglandin compound in an amount effective for improvement of encephalic function.
U.S. Pat. No. 5,284,858 discloses 13,14-dihydro-15-keto prostaglandins E having remarkable preventive effects against ulcers. Further, according to U.S. Pat. No. 5,284,858, 13,14-dihydro-15-ketoprostaglandins E have an advantage that they have none of the side effects which prostaglandin E intrinsically has, or can remarkably reduce such effects of the prostaglandin E. According to U.S. Pat. No. 5,284,858, 13,14-dihydro-15-keto prostaglandins E are effective for animal and human use for treatment and prevention of ulcers, such as duodenal ulcer and gastric ulcer.
U.S. Pat. No. 6,414,016 provides an anti-constipation composition containing a halogenated-bi-cyclic compound as an active ingredient in a ratio of bi-cyclic/mono-cyclic structure of at least 1:1. The halogenated-bi-cyclic compound in U.S. Pat. No. 6,414,016 is represented by Formula (I):

where X1 and X2 are preferably both fluorine atoms. According to U.S. Pat. No. 6,414,016, the composition can be used to treat constipation without substantive side-effects, such as stomachache.
WO2009/121228 discloses a Lubiprostone crystal, its preparation process, its pharmaceutical composition or kit, and its use for the preparation of a pharmaceutical composition for treating gastroenteropathy, especially constipation. According to WO2009/121228, the characteristic peaks of 2θ reflection angle in X-ray powder diffraction spectra of the crystal include 14.6±0.2°, 17.0±0.2° and 19.6±0.2°. According to WO2009/121228, the crystal has the advantages of high purity, stable property, and convenient storage and usage compared with amorphous Lubiprostone.